This invention relates in general to large containers. It deals particularly with large containers especially adapted for use in an underground environment.
In a self-contained sewage treatment system, for example, it is conventional to house the pumping equipment for the system in an underground container. Normally this equipment includes a plurality of pumps arranged side-by-side, in an elongated series. The protective container must necessarily have a generally horizontal, elongated configuration to house the equipment, as will readily be understood.
The simplest form a horizontally elongated container can take is, of course, a rectangular box-like structure having flat side, end, top, and bottom walls. Where the container is buried underground, however, the external pressure caused by the weight of the earth and effective on the flat walls necessitates substantially reinforcing the walls to prevent their collapse under stress. This is particularly true in a hollow container containing no liquid sewage or the like to counteract external pressures. The heavy reinforcement required in such a container necessarily increases the cost of the container substantially.
Elliptical containers have heretofore been used to house pumping equipment, but in order to properly utilize the available floor space in these types of containers, it has been necessary to provide additional internal piping in order to gain even reasonable utilization of the floor space available. Additionally, elliptical containers are severely restricted in practical length due to the fact that since the maximum width must be limited to approximately 12 feet to facilitate shipment, it is necessary to increase the shell plate thickness if the length of the container is to be increased.
The cellular container disclosed in U.S. Pat. No. 3,448,885 to J. W. Parks, and assigned to the same assignee of the present invention, increases the utilization of available floor space as compared to that of the elliptical container. However, this design requires a large shell plate thickness and increases the cost of fabrication due to the precision required in construction.
The object of the present invention is to provide a container structure for housing pumping equipment or the like underground which efficiently encloses space to form an essentially rectangular floor plan and wherein the container side walls are able to withstand relatively high compressive loads from the surrounding earth without excessive shell plate thickness or extensive reinforcing structures. The foregoing and other objects of the invention are realized in a container which includes a flat floor and ceiling, vertical side walls, and a semi-cylindrical end shell. The structure is reinforced sufficiently to avoid detrimental deflection primarily by rigid-frame beam rings around the flat-sided center section.
More precisely, a plurality of steel plates are fabricated to a rectangular center structure having a pair of substantially vertical side walls, a floor, and a ceiling. A semi-cylindrical end shell formed from steel plate is welded to the edges of the side walls closing off each end of the rectangular center structure. Rigid-frame beam rings around the flat-sided center section reinforce the structure. The rings comprise a pair of side ring members disposed on each side of the container which are welded to the ends of a ceiling ring member and a floor ring member to form a rectangular reinforcing ring around the rectangular center section. Corner stiffeners extend between the reinforcing rings at the top corners to prevent detrimental plate deflection between the rings due to stress. The cylindrical end shell segments may be of reduced thickness due to an inherent characteristic of the specific shell shape. Additionally, the reinforcing ring members may be sized as "fixed-end" members owing to the fact that the center structure is substantially restrained by the reinforcing rings. The hereinabove mentioned prior art structures are constructed primarily of "simple-supported" members which possess one and one-half times the moment of fixed-end members for the same uniformly distributed loading, which is the type of loading exerted on most underground pump station structures.